random-access memory
<storage> (RAM) (Previously "direct-access memory"). A data storage
device for which the order of access to different locations does not affect the
speed of access. This is in contrast to, say, a magnetic disk, magnetic tape or
a mercury delay line where it is very much quicker to access data sequentially
because accessing a non-sequential location requires physical movement of the
storage medium rather than just electronic switching.
The most common form of RAM in use today is built from semiconductor integrated
circuits, which can be either static (SRAM) or dynamic (DRAM). In the 1970s
magnetic core memory was used. RAM is still referred to as core by some
old-timers.
The term "RAM" has gained the additional meaning of read-write. Most kinds of
semiconductor read-only memory (ROM) are actually "random access" in the above
sense but are never referred to as RAM. Furthermore, memory referred to as RAM
can usually be read and written equally quickly (approximately), in contrast to
the various kinds of programmable read-only memory. Finally, RAM is usually
volatile though non-volatile random-access memory is also used.
Interestingly, some DRAM devices are not truly random access because various
kinds of "page mode" or "column mode" mean that sequential access is faster than
random access.
(1995-12-05)
Nearby terms:
RAMIS II « RAMTRON « random « random-access
memory » Random Access Memory Digital-to-Analog
Converter » randomness » random numbers
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